When Freddie is first seen visiting Doris' house, aluminum stick-on numbers are visible in the establishing shot, giving a street number. These numbers didn't' come onto the market until the 1960's- long after the time when the scene takes place.
When Freddie first goes to Doris's house, there is a motion activated spotlight on the house next door as he is climbing up the stairs. Motion detector activated lights weren't introduced till 1985, many years after this scene's time period.
In the "pacing" scene, as Quell goes from wooden paneled wall to window and back, the second time he goes to he wooden paneling, he breaks out a panel when he pounds it with rage. In the numerous successive shots, the wood panel is restored.
When Freddie starts undergoing processing at Helen's house, Lancaster Dodd has a handkerchief in his left hand but as the camera switches to a different angle, the handkerchief has shifted to his right hand.